The present study examined the neurological correlates of slot machine gambling by pathological and nonpathological gamblers while undergoing an fMRI scanning procedure. Twenty-two total participants were exposed to a series of losses, small wins, and large wins on a computerized simulated slot machine. Results indicate that the two types of gamblers responded differently to the various game options, and that an apparent "dose effect" exists when small and big wins are compared for pathological gamblers. Specifically more neural activation occurred in the dopaminergic pathway under conditions of large wins. These data suggest that a non-drug substance such as gambling may mimic typical drug-dose effects shown in previous literature. Implications for the treatment of pathological gamblers are discussed.